Suction ball filtration

The vessel and suction ball must be firmly clamped (see Figure 11) until filtration is complete. If necessary, the wall of the vessel may be washed down with a little solvent from a micropipette, even before filtration is complete. 

After the filtration, the filter end is cut off and, after being emptied, the suction ball is washed with solvent in the usual way. When dilution of the solution must be avoided, some of the solvent may be evaporated by heat, provided, of course, that further heating does not decompose the solute the-solvent vapor above the solution is sucked up into the empty suction ball, where it condenses and washes the walls of the ball this condensate is then removed from the ball in the usual way two or three repetitions of this process provide quantitative filtration. 

The classical use of a micro filter funnel and folded paper or cotton wool always leads to loss of material and when a suction ball is used, the filtrate contains neither threads from the paper nor colloidal portions of the clarifying agent. If the solute crystallizes in the suction ball during or after filtration, then, when filtration is complete and the filter end has been cut off, the suction ball is heated in a bath with the open capillary upwards until the crystals have redissolved. 

When recrystallization is effected in testtubes or pear-shaped flasks, the method used to separate the mother liquor must be adapted to the nature of the crystals produced. For well developed crystals a suction ball is used whose capillary end is drawn out to a fine capillary if the end of the capillary becomes blocked with crystals during the filtration, these can be removed by cautiously rotating the ball — but no air must be allowed to penetrate into the ball when the supernatant mother liquor has been sucked up, the crystals are washed with a few drops of solvent, which is again removed by means of the suction ball. 

Extraction of solid substances. For substances that are readily extracted it often suffices merely to digest or boil them with an appropriate amount of a suitable solvent. The solvent is then removed by centrifugation or by means of a suction ball adapted for filtration. Specialized apparatus103-107 is preferably used for substances that are difficult to extract or sparingly soluble. 

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